One of the more radical dreams of the true environmentalists (as opposed
to the anti-humanists who use environmentalism as a cover) is to convert
the world economy to renewable energy. They will not be fulfilled
until homes, factories and transport are using no fossil, nuclear or
other unclean, depletable energy supplies.

This is a tall order, one that humanity has not met since the discovery
of the useful properties of coal. Yet it remains worthwhile to
keep the goal in mind, if not for the environment, then for our political
and economic defense in the war declared against us by the
Islamofascists. Randall
Parker sets forth a standard by which we can measure our progress
in one sense: when the alternatives to oil are cheaper than oil,
the economic power of the Middle East will be beaten. Technology
is unlikely to retreat, while depleted oil fields will never be more
full than they are today.

The ideal scheme has always been the most expensive: the solar-powered
car versus the status quo. Photovoltaic cells are one of the most
expensive means of capturing energy from renewable sources, albeit also
one of the simplest and lowest-maintenance. If a car receiving power
from solar PV cells can deliver transportation at a lower cost per mile
than gasoline, the millennium will have arrived. But could the
millennium have sneaked in while we weren't looking? Let's take a
look at the figures.

The beauty of electric vehicles is that most of the required infrastructure
is already in place; we need no filling stations for new fuels or new
pipeline networks. The new vehicle designs are ready to hand: we
already have plug-free hybrid cars which attain 60 MPG and upwards, and if
we add bigger batteries to such a hybrid we can make a
plug-in hybrid or
CalCar. More batteries does
not just mean better acceleration and more efficient regenerative braking,
it also means some operation without the need for any energy besides the
stored electricity. We can build these cars today; we could (and
should) have been building them ten years ago (but the litany of the
sins of the California Air Resources Board is a rant for another day).

Suppose for a moment that we built such cars with today's technology and
tried to power them as much as possible with renewable energy. How
much would they cost to run?

The two major costs of the electric portion of such a vehicle are
electricity and battery degradation. Let's start with batteries.

The current price-leader technology for storage batteries is the old,
reliable lead-acid chemistry. It wins no prizes for energy density
or lifespan, but it can be made for substantial power density and it is
certainly cheap. Lithium-ion or fuel cells may be the ultimate
winner of the technology race forty years hence, but if we can make things
work with lead-acid we can get started immediately. We needed to
get started in 1990, so we have no time to lose.

Depending on the chemistry and technology, batteries are limited by both
cycle life and calendar life. If we take 3 years as a reasonable
period between battery replacements in a car and assume daily use, we
need approximately 1100 cycles from the battery if it is charged once
a day and 2200 cycles if it is charged twice a day (say, at home
overnight and again at work). If we refer to the cycle life vs.
depth of discharge curve below, we see that if we want 2200 cycles of
life we can discharge that model of battery by roughly 40%; if we
only need 1100 cycles we can discharge the battery by roughly 50%.

Current electric vehicles consume roughly 200 watt-hours per mile.
This seems to be a reasonable figure for conventional vehicles as well.
If the vehicle is required to operate for 30 miles on electricity alone,
it will require 6 KWH of electricity. At 50% DoD the battery pack
would have to store 12 KWH, or 15 KWH at 40% DoD.

A commercially-available deep-cycle battery storing a nominal 1.2 KWH
costs approximately $70 US at retail. If we assume that a battery
equivalent to the Yellow Top can be built at this price, plus bulk discounts
for production and purchase, we might see that drop to $60 or about $50
per KWH. A 12 KWH battery would cost $600; a 15 KWH battery would
cost $750. The cost of energy storage for 2200 cycles to 40% DoD
would be ($750/2200*6) = 5.7 cents/KWH; for 1100 cycles to 50% DoD, the
cost would be ($600/1100*6) = 9.1 cents/KWH. The corresponding
per-mile costs are 1.1 cents/mile and 1.8 cents/mile.

That takes care of the battery costs. What about the electricity to
charge them? Solar PV panels produce DC, so it seems reasonable
to assume a very high potential efficiency if they are being used to
charge batteries more or less directly. Assume the net efficiency
of battery plus charger is 80%, which yields 250 WH of PV output per
vehicle-mile of travel.

The actual price of solar PV depends on too many factors to account for
in an analysis this simple; however, the figure of $.25/KWH seems to
be reasonable for the day. If we assume values from $.30/KWH down
to $.20/KWH and run numbers, we get this range of projections:

$.30/KWH and 1100 cycles/3 years: 9.3 cents/mile.

$.30/KWH and 2200 cycles/3 years: 8.6 cents/mile.

$.25/KWH and 1100 cycles/3 years: 8.1 cents/mile.

$.25/KWH and 2200 cycles/3 years: 7.4 cents/mile.

$.20/KWH and 1100 cycles/3 years: 6.8 cents/mile.

$.20/KWH and 2200 cycles/3 years: 6.1 cents/mile.

If we assume wind or hydro power may be available at $.10/KWH retail,
the figures look even better:

$.10/KWH and 1100 cycles/3 years: 4.3 cents/mile.

$.10/KWH and 2200 cycles/3 years: 3.6 cents/mile.

At this writing the retail price of regular unleaded gasoline is pushing
$2.20/gallon in California. If the competition is a conventional
internal-combustion engine vehicle burning regular gas at that price, I get
the following energy costs for various levels of economy:

12 MPG (typical big SUV): 18.3 cents/mile

16 MPG (typical medium SUV): 13.8 cents/mile

20 MPG (typical small SUV): 11 cents/mile

27.5 MPG (CAFE limit for passenger cars): 8 cents/mile

35 MPG (economy car): 6.3 cents/mile

60 MPG (2004 Toyota Prius, city rating): 3.7 cents/mile

From the look of it, solar PV feeding plug-in hybrid cars can already
deliver transportation to Californians more cheaply than any ICE-powered
vehicle getting less than 20 MPG. If solar PV costs 20 cents/KWH
and the vehicle runs its batteries for 2200 cycles between replacements,
the cost is already par with a 35-MPG economy car. And if you
assume the availability of wind or hydro power at 10 cents/KWH for charging, the
plug-in hybrid can push energy-cost parity with the Prius.

It looks like the millenium may already be here. It's time to
wake up and smell the coffee.

Many thanks to the Institute for Analysis of
Global Security, who compiled many of these links and did a fine job of
documenting much of what I've been thinking about for the last several years
before I found out about them. Also thanks to
Randall Parker, who brought them
to my notice.